The present invention relates to a method of encoding and decoding the video data of an image sequence. Such methods commonly involve raster-scanning all images and subsequently digitizing the video signals thus obtained. In the simplest case, the image sequence is transmitted by transmitting the digitized video signals successively. This method of encoding requires a data channel of very high capacity, the needed capacity depending on resolution and frame rate. The same applies if the data of such image sequences have to be stored, in which case suitable memory capacity has to be made available for storing the data stream.
Encoding techniques are known which exploit redundancy which naturally occurs in the video data to reduce the volume of the data stream. In the case of single frames and image sequences, advantage is taken of the fact that the frame or image usually contains large-area structures besides find details, and that within these large-area structures, high resolution is not necessary. In large-area structures, adjacent picture elements in a horizontal, vertical or arbitrary direction differ only in the marginal areas of these structures. The similarity is even greater if two successive single frames of an image sequence are compared. Some conventional methods of encoding exploit these similarities, e.g., in differential pulse code modulation (DPCM).
Data reduction during encoding is also possible if, in addition to the pure video data of an image sequence, any motion within the image sequence is taken into account. This permits an estimation of the direction in which the respective picture elements are likely to move. From this transmitted motion information, better estimates can be determined at the receiving end for the single frames to be reconstructed. Conventional coding techniques for this purpose provide more or less accurately reconstructed image sequences depending on the method and amount of circuitry used. Such methods, including movement detection, are described, for example, in the Jae S. Lim, "Two-Dimensional Signal and Image Processing", Prentice-Hall International, Inc., 1990, particularly Chapter 9.6.2, "Motion-Compensated Image Restoration", pages 570-575.
European Patent Specifications EP-B 0 154 125 discloses a method for the motion-adaptive interpolation of television-picture sequences, an arrangement for carrying out the method, and a use of the method. There, individual parts of a picture sequence are omitted during transmission. By means of motion estimators it is determined which parts of the picture are stationary or moving and which stationary parts of the background are covered or made visible by the moving parts of the picture.
Since motion estimation for video signals is accomplished by means of complicated algorithms, which must be performed in real time, motion estimation for high-resolution television signals has so far been considered only at the transmitting end. The motion information is transmitted by the transmitter as a coded motion vector. At the receiver, the complete picture sequence for the high-resolution television picture is reconstructed from this motion information by means of simple adaptive filter circuits.
Advances in circuit integration as a result of digitization make it possible to use complex signal-processing techniques, which were hitherto employed only at the studio or transmitter end, in consumer equipment. For example, a further reduction of the video data to be transmitted can be obtained if the relatively large amount of motion information required to form the motion estimates at the receiving end need not be transmitted.
It is the object of the invention as claimed to provide a method of encoding and decoding video data of an image sequence which manages without the transmission of independent motion information and, nevertheless, ensures high-quality rendition.